1. Yes
2. Central
3. Multiple
4. See #2
5. Hm. Good question, and I don't know the answer. The bigger problem would be if that update broke Volcano.

Would
the server also need a copy of the custom age's .fni and .prp files?
Or are those on the Volcano data server
If there are multiple UU shards with fan-created content, will the
client list all these available shards, or only one shard?
Is the Volcano Dataserver in one central location, or does each UU
shard server with fan-created content have a Volcano Dataserver
running on it?
If Cyan updates their data server again after the Volcano Dataserver
is up and running (along with a UU shard), how will the Volcano
Dataserver be updated accordingly?
If there are multiple UU shards with fan-created content, will the
client list all these available shards, or only one shard?
If the multiple UU shards have different sets of fan-created content
on it, what will happen if the client switches from one shard to the
other?
If Cyan updates their data server again after the Volcano Dataserver
is up and running (along with a UU shard), how will the Volcano
Dataserver be updated accordingly?
A supplimental dataserver to Cyan's dataserver will be introduced, which supplies the patched client with the new ages' .PRP and .FNI files
4.b.2) The following additions to the Vault will be made by an admin (e.g. via the Vault Manager):
GlobalInbox folder
... \-- Text Node: [ServerInfo]
......... |-- Chronicle: VolcanoEnabled = 1
......... \-- Chronicle: VolcanoAges = (List of ages available on this shard, separated by spaces)
4.c. CLIENT MODIFICATIONS. Anyone wishing to visit a UU shard containing fan-created content must install a separate URU: Ages Beyond Myst or URU: Complete Chronicles installation on their client machine. Then, they must apply a "Volcano patch" to the standard URU client which will make the modifications listed below:
4.c.2) All available fan-made ages are downloaded either from the Dataserver or included in the patch program (depending on what version of the patcher is downloaded and how new the age is), and are added to the "dat" folder of the URU installation.
the patched client with the fan-created ages' files (.AGE, .SUM, .P2F, .PRP and .FNI)
Anyone wishing to visit a UU shard containing fan-created content must install a separate Until Uru installation on their client machine. Then, they must apply a "Volcano patch" to the standard UU client which will make the modifications listed below:
The file Volcano.pak, which contains python modifications for the Relto Bookshelf to enable clients to visit the fan-created ages from the Volcano book, is placed in the Python folder of the UU installation. The Volcano book will check the selected UU server's vault and will only display the fan-created ages that are available on the UU server.